1. Field of the Invention
The invention in general relates to silicon carbide technology and more particularly to the preparation of a silicon carbide wafer for production of a silicon carbide semiconductor device.
2. Description of Related Art
Silicon carbide is being used extensively as a semiconductor material for various electronic applications. Semiconductor devices of silicon carbide have the ability to operate at higher voltages and temperatures than conventional silicon or gallium arsenide devices thus providing for higher power devices with reduced cooling requirements. Silicon carbide metal-semiconductor field effect transistors (MESFET) have been made to operate at power densities two times the highest reported for a GaAs MESFET and silicon carbide static induction transistors have operated at four times the power density of comparable silicon devices for high frequency microwave radar systems.
Electronic applications for silicon carbide semiconductor devices include compact, low cost airborne, ship and ground radars, aircraft engine and flight controls, electric tank and ship propulsion systems and satellite communications, to name a few. In the commercial sector, silicon carbide may be used in the field of high definition television, industrial power conditioning, nuclear control and instrumentation and electric vehicle power trains.
Silicon carbide semiconductor devices are fabricated utilizing a thin silicon carbide wafer which is obtained from the sawing of a silicon carbide crystal boule. The sawing operation results in a wafer surface which, although appearing smooth, actually is damaged and contains microscopic scratches completely unacceptable for a subsequent epitaxial growth procedure. Due to the damaged surface the resulting semiconductor device would either not operate or operate at reduced efficiency.
Accordingly, the silicon carbide wafer surface must be highly polished to substantially eliminate all traces of any scratches and surface defects. In view of the fact that silicon carbide is twice as hard as silicon, the exact process for polishing silicon wafers is unsuitable for silicon carbide. Conventional optical polishing techniques may take ten days or more to achieve an acceptable surface finish for silicon carbide wafers.
The present invention reduces silicon carbide wafer polishing time to a matter of hours.